The present invention deals with the field of fireproofing buildings and, particularly, fireproofing between a floor such as a concrete slab and a curtain wall positioned immediately outwardly therefrom. A space is commonly defined between the outer edge of a floor and the curtain wall normally formed by vertical and horizontal framing members with curtain wall panels extending therebetween which are normally transparent and formed of glass. The present invention provides a means for sealing this space or safing gap defined between the outer edge of the floor and the curtain wall for firestopping thereof and preventing the spread of fire vertically between floors.